Known tandem drive vehicles, for example, use suspensions incorporating equalizing beams and leaf springs to cushion road shocks and to distribute weight between the tandem drive axles, thereby improving traction. The springs are generally mounted on saddle assemblies above the equalizing beams and connected at the front ends to front spring hangers with spring eye pins or spindles (hereinafter called "spring pins") through the spring eyes. The rear ends of the springs need have no rigid attachment to the rear spring hangers and may be free to move forward and backward to accommodate spring deflection. The rear hangers may be provided with cam surfaces which allow for this movement of the spring. Spring hangers may be affixed to the frame or chassis of the vehicle by conventional fixing means such as bolts, washers and nuts.
It is generally seen advantageous the tandem drive axles be parallel to each other and properly aligned with respect to the longitudinal axis of the truck frame or chassis. Prior suspension systems have been found wanting in satisfactory means for adjustment of the alignment of the axle with respect to the vehicle frame of chassis. The need for such adjustment has arisen in the last 2-3 years as a result of improvements in alignment measurement techniques, especially as a result of using laser-based equipment. If the axles and the wheels are properly aligned with the longitudinal axis of the vehicle frame, tire wear may be minimized and significant savings in fuel comsumption may also be achieved.
Two methods have been developed in an effort to provide some form of alignment adjustment. Those methods have related on the one hand to altering the position of the saddle assembly with respect to the leaf spring assembly and on the other hand, to fitting an eccentric adaptor at the ends of the equalizing beams where they are attached to the vehicle axles. The former method can be time consuming and arduous as it usually involves disassembling the saddle assembly and the leaf spring assembly.